Diphenylamine is well known to have a variety of uses, including as a rubber antioxidant and accelerator, a stabilizer for plastics, as well as an intermediate for pesticides, explosives, dyes and antioxidants. Conventionally, diphenylamine is produced by contacting aniline with an alumina catalyst at very high temperatures of more than 450.degree. C. Thus, Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 2, page 311 (3d Ed., 1978) discloses that "Passing aniline vapor over activated alumina under pressure and at a temperature above 450.degree. C. gives diphenylamine".
Somewhat similarly, U.S. Pat. No. 3,118,944 to Addis discloses a process for producing diphenylamine by reacting aniline with an alumina catalyst having a surface area of some 100-400 square meters per gram and a pore volume of about 0.50 cubic centimeters per gram. It is particularly noteworthy that Addis indicates (at Col. 3, lines 32-33) that "However at appreciably below 450.degree. the result is too poor to be useful".
Conventional commercial processes typically employ alumina catalysts having more than one-third of their total porosity (by volume) in the form of comparatively small pores (having a diameter of between about 36 and about 60 Angstroms) and an initial sulfur content (as measured in the form of SO.sub.4) in excess of 3 weight percent. Typically, however, such sulfur content may decrease during the reaction process.
Although such known processes are effective in converting aniline into diphenylamine (and ammonia) at yields of up to about 90% (based upon the conversion of aniline), it would nonetheless be desirable to possess a process for producing diphenylamine from aniline at increased efficiency.
Moreover, it is evident that such high temperature prior art processes require the consumption of relatively large amounts of energy and are thus economically undesirable. Thus, it would be desirable to possess a process for producing diphenylamine which required reduced amounts of energy or alternatively, which produced diphenylamine more efficiently at such higher temperatures.
Accordingly, it is an object of this invention to provide a process for the production of diphenylamine from aniline, which process exhibits increased efficiency of conversion.
It is a further object of this invention to provide a process for the production of diphenylamine, which process requires reduced amounts of energy consumption to produce a given amount of product.
The above objects and additional objects will become more fully apparent from the following description and accompanying Examples.